This invention relates to a lead-free metallic body solder and, more particularly, to a tin-base body solder containing copper, iron and preferably zinc.
Body solder is traditionally a lead-base alloy that is applied to a fabricated steel surface to fill depressions about a welded seam or to repair a dent, and thereby form a smooth decorative surface. Lead-base alloys form a spreadable, workable paste over a wide range of moderately elevated temperatures, and, upon cooling, form a dense, tightly adherent fill suitable for surface finishing and painting in conjunction with the surrounding steel surface. However, lead requires careful handling in a plant environment.
U.S. Patent application Ser. No. 113,559, filed Jan. 21, 1980, now U.S. Pat. No. 4,248,905, and assigned to the assignee of the present invention, describes a lead-free tin-base body solder comparable to conventional lead-base solders. The body solder consists of 10 to 25 weight percent copper, 1 to 7.5 weight percent zinc and the balance tin, and forms a spreadable paste when heated above about 210.degree. C. For convenient handling, the alloy is cast and extruded into a bar. It has been found that the formation of the desired paste is particularly sensitive to rapid cooling of the casting, preferably at a rate between 10.degree. to 100.degree. l C. per second, so as to form a relatively fine dendritic microstructure. When reheated, the rapidly cooled casting produces fine particles suspended in liquid phase to form the desired paste. However, it is difficult to achieve the desired rapid cooling in large-scale production.
Therefore, it is an object of this invention to provide a lead-free body solder composed of a tin-base alloy that is readily castable and forms when reheated a spreadable paste whose properties are relatively insensitive to the casting cooling rate. The predominantly tin alloy contains copper, iron and preferably zinc. The paste displays properties comparable to lead-base alloys or rapidly cooled iron-free tin-base alloys and is suitable for filling a depression in a fabricated steel surface.